High-altitude refers to locations that are significantly above sea level, typically starting at around 2,400 meters (7,874 feet). At these elevations, the air pressure decreases, leading to lower oxygen levels, which can affect human health and physical performance. High-altitude environments are often found in mountainous regions, such as the Himalayas or the Andes. People living or traveling in high-altitude areas may experience altitude sickness, which can cause symptoms like headaches, nausea, and fatigue. To adapt, the body may produce more red blood cells to improve oxygen transport. Activities like mountaineering and skiing are popular in these regions, attracting adventurers and tourists alike.